Next using well-known identity (Abel formula) relating 5
dilogarithms [1]}, [2]}
\(\frac{1}{2} \, \log ^2\frac{s}{u} &+&{\rm Li}_2\biggl (1+\frac{t}{s}\biggr )+ {\rm Li}_2\biggl (1+\frac{t}{u}\biggr ) \nonumber \\&-& {\rm Li}_2\biggl (1+\frac{Q^2 t}{s u}\biggr )+ {\rm Li}_2\biggl (1-\frac{Q^2}{s}\biggr )+ {\rm Li}_2\biggl (1-\frac{Q^2}{u}\biggr ) = 0 \,,\) 
